1. Field of the Invention
This invention relates to a process for recovering hydrocarbons from a hydrocarbon-bearing formation. More particularly, this invention relates to a tertiary hydrocarbon-recovery process in which the formation is first treated with a vinylpyrrolidone polymer followed by injection of an aqueous surfactant solution and finally recovering hydrocarbons via the production well. Optionally, an aqueous drive fluid is injected into the formation.
2. Prior Art
The production of petroleum products is usually accomplished by drilling into a hydrocarbon-bearing formation and utilizing one of the well-known recovery methods for the recovery of hydrocarbons. However, it is recognized that these primary recovery techniques may recover only a minor portion of the petroleum products present in the formation particularly when applied to reservoirs of viscous crudes. Even the use of improved recovery practices involving heating, miscible flooding, waterflooding and steam processing may still leave up to 70-80 percent of the original hydrocarbons in place.
Thus, many large reserves of petroleum fluids from which only small recoveries have been realized by present commercial recovery methods, are yet to reach a potential recovery approaching their estimated oil-in-place.
Waterflooding is one of the more widely practiced secondary recovery methods. A successful waterflood may result in recovery of 30-50 percent of the original hydrocarbons left in place. However, generally the application of waterflooding to many crudes results in much lower recoveries.
The newer development in recovery methods for heavy crudes is the use of steam injection which has been applied in several modifications, including the "push-pull" technique and through-put methods, and has resulted in significant recoveries in some areas. Crude recovery of this process is enhanced through the beneficial effects of the drastic viscosity reduction that accompanies an increase in temperature. This reduction in viscosity facilitates the production of hydrocarbons since it improves their mobility, i.e., it increases their ability to flow.
However, the application of these secondary recovery techniques to depleted formations may leave major quantities of oil-in-place, since the crude is tightly bound to the sand particles of the formation, that is, the sorptive capacity of the sand for the crude is great. In addition, interfacial tension between the immiscible phases results in entrapping crude in the pores, thereby reducing recovery. Another disadvantage is the tendency of the aqueous drive fluid to remove additional gas by diffusion from the in-place oil thus further reducing the already lowered formation oil volume and increasing the viscosity of the oil.
There is a definite need in the art for a water-flooding process in which the disadvantages discussed above are largely eliminated or avoided.